Gas electrodes, in and with which a gas is passed in contact with a suitable electrode conductor in the presence of an electrolyte solution, are well known. Many modern gas electrodes are made to be porous and to have catalytically-active surface areas, including the walls of the interstitial passageways within the electrode body. In this way, there can be realized maximization of the available and effective surface area for given unit geometric volumes of the electrode configuration.
Such general type and style of electrode construction is especially advantageous for the oxygen gas-bearing, depolarized electrodes, particularly cathodes, that are well adapted for the electroreduction of oxygen in alkaline media.
The usage technique applied with such electrodes often involves passage of the oxygen-bearing gas through the porous electrode body for contact with the involved electrolyte interstitially therewithin and/or at and on the electrolyte-contacting face or wall of the electrode body. The indicated practice is desirable for electrolyzing functions and, conversely, as well as for operation in the galvanic mode as in fuel cells. Oxygen gas-bearing depolarized cathodes so made and operated are particularly attractive for utilization in chlor-alkali and the like or equivalent manufacturing cell operations.
A great and impelling reason (although other benefits also accrue) for employing oxygen gas-bearing, depolarized porous electrodes to electrolyze common salt brine into chlorine and caustic, and for analogous production purposes, is economic. Potentially significant savings in power requirements for given electrolysis workings are anticipatable due to substantial reductions potentially achievable in needs for applied electrical consumption when such electrodes are utilized. This is evident in comparison of voltage levels for the involved electrochemical reactions, taking into account that conventional cells already are usually operated at quite low voltages; the cathodic reactions (disregarding overvoltage effects) respectively being:
In traditionally common chlor-alkali cells EQU 2H.sub.2 O+2e.sup.- .fwdarw.H.sub.2 +2OH.sup.-, with E.degree.=-0.828 volt; and
With the oxygen-gas depolarized cathodes EQU O.sub.2 +H.sub.2 O+4e.sup.- .fwdarw.4OH.sup.-, with E.degree.=only 0.401 volt;
there being a consequent theoretically attainable saving of 1.229 volts in the difference.
Literally from their inception and classically, oxygen electrodes have been catalyzed by various precious and semi-precious metals and compounds thereof, such as gold, osmium, palladium, platinum, silver and so forth and their alloys, oxides and other compositions. These noble metals are not only in generally scarce supply for other than jewelry adornments and ornamentations and/or monetary purposes, but are inherently extremely expensive for industrial applications. Because of this, their consumption for electrode preparation is carefully controlled and extended to the greatest possible extent; this usually being done so as to minimize total quantity usage by deposition thereof in the form of platings or other applied layers or coatings over a suitable substrate, such as porous nickel plaque.
It would obviously be desirable to have a more abundant and readily-available, less costly, catalytically-active material adaptable to electrode construction, especially for satisfactory use in alkaline media as an oxygen gas-bearing depolarized cathode for electrolysis or galvanic mode purposes. Manganese is one such substance; being in good, relatively-inexpensive supply so as to permit more copious use thereof in and for electrodes. This, at least superficially and apparently, would seem to have ensured the provision of reliable and effective electrodes based on manganese made in straightforward and uncomplicated fashion.
Surprisingly, however, the stated expectation is not the case. The heretofore known electrodes utilizing some form of manganese either employ the oxides, carbides or other compounds of the metal as coatings or fillers for the electrode or resort to treatment of the metal merely as a substrate carrier for another physically-blended, catalytically-active, amalgamated sort of additament or necessitate using a metallurgical alloy of the metal for electrode fabrication. U.S. Pat. Nos. 3,088,851; 3,496,021; 3,607,787; 3,616,323; 3,753,782; and 3,778,307 as well as Chemical Abstracts, 78:79013y are exemplary of one or another form of these practices which, by one or another means of complication, employ and teach use of only either reacted or alloyed manganese for electrodes.